Typically used for
Thermostat
Floor heating
Heating
Energy saving
Valves
Key Features
Valve control - precisely manages the valves in your underfloor heating system (supports up to 2A resistive load or 1A inductive load).
Dry contant relay - can signal your gas boiler, pellet stove, or other heating sources to turn on and off.
Supports electric underfloor heating - the thermostat can signal a connected Shelly relay to switch the heating on or off automatically based on temperature settings.
Anti-freeze function - maintains a minimum temperature during long absences to prevent pipes from freezing and bursting.
Humidity sensor
Temperature & humidity offsets - adjust the thermostat’s readings to make them more accurate.
No hub required! Wi-Fi and Bluetooth connectivity
Wi-Fi Range Extender & BLE Gateway
Simple & intuitive interface
Powered by Shelly - equipped with a Shelly chip, offering full Shelly capabilities
Highly compatible! Easy control through the Shelly Smart Control app, most automation platforms and open documented protocols. Support for Alexa and Google Home coming soon.
Device identification
Device type: Smart thermostat
Device model: ST1820-W
Main features
Supports up to 2A resistive load or 1A inductive load.
Dry contact relay
Supports electric underfloor heating
Anti-freeze function
Humidity sensor
Temperature & humidity offsets
Wi-Fi and Bluetooth connectivity
Connectivity
Wi-Fi
Bluetooth
User interface
Knob to access parameters and set temperature.
Press the button to turn on/off device, or to confirm the parameters.
Specification | Value |
|---|---|
Product model | ST1820-W |
Size (H x W x L) | 85.8 x 85.5 x 12 mm (for more information see Fig. 1: Device dimensions) |
Power input voltage | 90-240 V AC, 50/60 Hz |
Wireless protocol | Wi-Fi 802.11 b |
Working humidity | 5 to 95% |
Temperature measurement accuracy | ±0.5°C |
Humidity measurement accuracy | ±5% |
Working environment | -10°C to 55°C |
Load current | 2 A resistive load, 1 A inductive load |
Fig. 1: Device dimensionsWiring diagram
"R1" : Connected to the floor heating valve
"L" : Connected to live line of power supply
"N": Connected to the floor heating valve
"N": Connected to neutral line
"C1"/"C2" is a dry contact as a control signal for turning gas boiler or other heat source equipment on/off
What are the differences between the different generations of Shelly products?
Each new generation adds more power, memory, and features:
Gen 1 offers basic control;
Gen 2 (Plus Series, Mini Series, Pro Series) adds Bluetooth, scripting, and better security;
Gen 3 improves performance, adds Matter (starting from firmware version 1.6.0 or newer) and advanced monitoring;
Gen 4 offers multi-protocol connectivity, featuring Wi-Fi 6, Bluetooth, Zigbee, and Matter.
Can I control the device via Bluetooth?
No, the protocol is used only for device inclusion, allowing for quick and easy setup through the Shelly Smart Control app.
For bluetooth control it is required to have another Bluetooth device such as Shelly BLU Button or Shelly BLU Motion to interact.
Additionally, Shelly devices can function as a BLE gateway, bridging Shelly BLU devices to your Wi-Fi network.
Is it possible to use the device without a hub?
Yes, Shelly devices (except for Wave devices) operate independently without the need for a hub. They connect directly to your Wi-Fi network, and you can control them via the Shelly Smart Control app, web interface, or through integrations with platforms like Google Home, Alexa, Home Assistant and Samsung SmartThings.
Use cases
Control the temperature at home
The thermostat gives you full control over your underfloor heating, directly adjusting the valves to regulate heat distribution. Using its dry contact relay, it can activate heat sources like gas boilers or pellet stoves.
Electrical underfloor heating with another Shelly
Control your electric underfloor heating by signaling a connected Shelly relay to turn on or off based on the room’s temperature and humidity.
Full safety of your heating installation
The Anti-freeze function of the thermostat ensures that even if you're away from home, your heating installation is safe. It ensures temperature in the room never gets too low thus preventing damage to the heating pipes and your home.
Lower Energy Bills
Equipped with full Shelly capabilities, this thermostat will save energy without sacrificing comfort.